Saliva is a clear liquid secreted into the mouth by various glands and is essential for maintenance of oral function and health and performs various critical functions in the oral cavity. For example, saliva neutralizes the acids that promote dental caries and helps in the re-mineralization of areas of incipient caries development. Further, saliva contains specific antimicrobial agents that assist in reducing the number of bacteria in the oral cavity by several means, such as dilution, aggregating factors, microbicidal enzymes and so forth. Moreover, salivary glycoproteins reduce intraoral friction between different oral structures such as teeth, cheek, tongue and lips by lubricating the hard and soft tissues. Also, saliva aids in swallowing by facilitating bolus formation, and salivary enzymes such as lipase and amylase start the digestion of food. Moreover, perception of taste is facilitated by salivary dilution.
Saliva is produced by the salivary glands. Every normal human has three pairs of major salivary glands: the parotid glands that are located under the skin of the cheeks, the submandibular glands and the sublingual glands, which are located at the bottom of the mouth. In addition, hundreds of minor salivary glands are spread throughout the oral cavity lining. According to C. Dawes in “The contribution of oral minor mucous gland secretions to the volume of whole saliva in man”, Archs Oral Biology, 1973, the parotid, submandibular and sublingual salivas comprise more than 90% of the whole saliva present in the mouth. The secretion of saliva is regulated by the salivary reflex that is part of the autonomic nervous system of body. Afferent fibers that are part of cranial nerves carry various signals such as those for tasting, chewing or perceiving a foreign body from the oral cavity to the brain. In response to the signals, efferent fibers that run through the same or others nerves, release stimulatory commands to all salivary glands. This phenomenon is known as ‘salivary reflex’. The only nerve exposed to the oral cavity lining that carries both types of fibers (afferent and efferent) is the lingual nerve. The lingual nerve directly stimulates the submandibular glands and the sublingual glands. Further, the lingual nerve indirectly stimulates all salivary glands through the salivary reflex.
Xerostomia or dry mouth symptom is a very common problem. According to estimates, about 10% of the adult population over 25 years of age may complain of it at some time, and it is a serious health and quality of life problem for about 1-2% of the adult population. Typically, xerostomia may be associated with salivary gland dysfunction. However, xerostomia may not always reflect the actual salivary gland performance. See “Xerostomia: evaluation of a symptom with increasing significance”, Journal of American Dental Association, 1985, Philip C. Fox et al. According to Wolff A et al, in “Major salivary gland output differs between users and non-users of specific medication categories”, Gerodontology, 2008, xerostomia is more closely related to the function of the submandibular and sublingual glands than the parotid glands. Chronic xerostomia can be caused by diseases such as Sjögren's syndrome, nerve damage, certain medications, therapeutic irradiation and or by other chronic diseases. Xerostomia can cause difficulty in eating dry foods, swallowing, speaking and wearing dentures. Moreover, xerostomia increases the number of wake-up episodes during sleeping time in a need to moist the mouth, susceptibility to dental caries, oral pain and frequent infections.
Generally, the treatment of xerostomia is difficult and the currently available treatments are not satisfactory. Symptomatic treatments include mouthwashes, gels and local intra-oral sialogogues (salivation stimulators) such as sugarless hard candies or chewing gum. However, such treatments provide only short-lasting effects that fade after a few minutes of treatment. Further, in case of patients having xerostomia due to a non-pharmacologic cause, ingested systemic sialogogues (if not contraindicated) may be helpful. However, ingested systemic sialogogues have adverse effects such as perspiration, flushing, urinary urgency and lacrimation.
It is well known that stimulation of the autonomic nerves associated with the salivary glands by low power electric stimulation can increase salivation output of the salivary glands. Furthermore, due to the dual type of fibers carried by the lingual nerve (afferent and efferent), stimulating the vicinity of this nerve, i.e. the mucosa behind the lower third molar, results in both, (a) direct impulses to the submandibular glands and the sublingual glands nerve, and (b) indirect stimulus through the salivary reflex to the other major and minor salivary glands in the oral and pharyngeal regions. As a result, the salivation is increased (see, “Electrostimulating device in the management of xerostomia”, Oral Diseases, 2007, Strietzel FP et al.). Placing a module, or part of it, inside the intra-oral environment to provide electric stimulation requires unique manufacturing methods in order to guarantee the functionality and durability of the device over time. Generally, any object placed within the oral cavity must withstand constant wetness (of saliva and intake liquids), mastication forces, forces applied by the tongue and other oral muscles, varying pH levels from 1 to 9, ambient temperature of 37° C., and temperature variations ranging between +0° C. and +65° C. due to cold and hot drinks intake.
Existing techniques as disclosed in U.S. Pat. Nos. 4,519,400 and 4,637,405 assigned to Brenman et al., teach a stimulator for inducing salivation by neural stimulation. The stimulator includes a housing that encloses electronic signal generating means and electrodes for applying a signal to neurally sensitive areas of the oral cavity to induce salivation. The stimulator is coupled to the hard palate of a user and is held in place by connecting it to a tooth of the upper jaw. However, this configuration causes discomfort to the user. Further, the user's ability to speak, eat and/or drink are affected severely. Moreover, the signals do not stimulate the lingual nerve.
Another existing technique as disclosed in EP Pat Application No. 278,847 assigned to Jaffreo Albert, teaches the application of an electrical signal to neurally sensitive locations by an apparatus. The apparatus is in the form of a pellet made of a non-conductive material with electrodes on the opposite faces of the apparatus. The apparatus has no means of firm attachment within the oral cavity and is only held freely within the pral cavity. Further, the apparatus can be moved from one place to another in the oral cavity by aid of the tongue. However, there is a risk that the apparatus may be accidentally swallowed into the gastro-intestinal tract or aspirated into the lungs by the user.
Yet another existing technique as disclosed in U.S. Pat. No. 6,230,052 assigned to Wolff et al. teaches an implantable device for inducing salivation by neural stimulation at neurally sensitive location within an oral or perioral tissue of the user. The device includes a housing adapted to be permanently implanted within the oral or perioral tissue. The housing includes an enclosure for engaging an electrical signal generator. Further, the signal generator includes a power source and electrodes. The electrodes form an electrical contact with neurally sensitive location of the oral or perioral tissue, the stimulation of which by electrical energy can induce salivation. However, the device needs to fixed by an invasive procedure, requiring implantation as essential component in the oral cavity. Moreover, the implant is a costly component and requires a surgical procedure involving considerable risk to the user.
Another existing technique as disclosed in U.S. Pat. No. 7,477,947 assigned to Pines et al. teaches electrical detection of a lack of saliva in the oral cavity and electrically stimulating the oral cavity to induce the production of saliva from the salivary glands. However, electric detection and measurement of saliva quantity and oral moisture and comparing the obtained measure to a moisture limit value are essential elements needed to deliver the electrical impulses. An additional limitation of this patent is the need of the intraoral device to be configured so as to be fixable to at least one tooth within an oral cavity of an individual.
Yet another existing technique as disclosed in PCT Pat. Application No. WO 2006/100238 to Michel Rochat et al., teaches a salivary stimulation device having an electronic circuit that generates and transmits electric signals by means of stimulation electrodes. The aforementioned device takes the form of a channel that is preferably made of a transparent thermoplastic material. The electronic circuit is embedded at one edge of the channel. According to the invention, only the free ends of the electrodes extend outwardly from the channel in order to be brought into contact with the oral cavity and to stimulate the salivary glands of the user. However, the device may be specially designed for the oral cavity of the user. An existing technique for manufacturing and testing of intra-oral embedded devices is disclosed in U.S. Pat. Application No. 2009/0210032.
In light of the above discussion, techniques are desired for treating xerostomia devoid of the above limitations.